JP6261445B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a developing device that develops an electrostatic latent image formed on an image carrier by an electrophotographic method, an electrostatic recording method, or the like to form a visible image.

  The electrostatic latent image formed on the image carrier is developed into a toner image by a developer containing a toner and a carrier made of magnetic particles, and the toner image is transferred to a recording material, and then heated and pressurized. An image forming apparatus that fixes a toner image to a recording material is widely used.

  The developing device frictionally charges the toner and the carrier by rotating the screw member and transporting the developer while stirring in the circulation path in the developing container. The developer containing the toner and the carrier gradually deteriorates the charging performance of the carrier as the carrier that is not consumed by the image formation continues to circulate while receiving friction in the developing container. For this reason, in Patent Document 1, a new carrier is replenished in the developing container, while a part of the developer conveyed through the discharge port provided in the circulation path is overflowed and discharged. This ensures the average charging performance of the carrier in the developer.

  Further, in Patent Document 2, the circumferential or outward radial force acting on the developer by the rotation of the screw member in the region facing the developer discharge port is configured to be smaller than in other regions. An improved developing device has been proposed. As an embodiment, in a region facing the developer discharge port, a configuration in which the blade of the screw member is made small or a configuration in which the blade is omitted is shown. As a result, it is possible to suppress the developer from jumping up by the blades of the screw member in the developer container facing the developer discharge port, and to discharge only the developer that is truly surplus.

  Moreover, in patent document 3, the screw blade | wing of the area | region which opposes a developer discharge port is abbreviate | omitted, Furthermore, the developer of the area | region along a developer discharge port is supplied to the area | region with rotation of a screw blade | wing. A rib for stirring or shaking is locally formed. The rib has a smaller diameter than that of the screw blade, and by taking such a configuration, the developer in the region facing the developer discharge port is vibrated. As a result, in the configuration in which the screw blades in the region facing the developer discharge port are omitted, or in the configuration in which the developer is prevented from jumping up by the screw member as in Patent Document 2, the fluidity of the developer is caused by the above-described vibration. Regardless of this, stable discharge is possible.

JP 59-1000047 A JP 2000-112238 A JP 2012-234153 A

  However, a small-diameter screw blade is installed around the screw shaft or a small-diameter rib for vibration is installed in a portion facing the developer discharge port. The developer cannot be splashed by the small diameter screw blade or the small diameter rib itself. However, the developer is wound up by the terminal portion of the screw blade on the upstream side of the portion where the screw blade in the region facing the developer discharge port is omitted. The developer collides with these small diameter screw blades and small diameter ribs depending on the installation phase of the small diameter screw blades and small diameter ribs. As a result, there is a problem that the developer is further splashed and overflows from the developer discharge port (see FIG. 5).

  Devising the size of the small-diameter screw blades and small-diameter ribs prevents the developer from jumping up by the ribs themselves. However, the developer splashed by the terminal end of the screw blade upstream of the portion where the screw blade is omitted is further splashed by the small-diameter screw blade or the small-diameter rib. As a result, the developer leaks due to splashing. In this way, the developer that does not need to be discharged from the developer discharge port overflows due to the jumping up by the small-diameter screw blade or the small-diameter rib. As a result, the amount of the developer in the developing container gradually decreases, and there is a possibility that density unevenness occurs due to the insufficient coating of the developer on the surface of the developing sleeve.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object of the present invention is to provide a developing device that suppresses the developer's jumping up and discharging by a protrusion disposed in a region facing the developer discharge port. It is.

  In order to achieve the above object, a typical configuration of a developing device according to the present invention includes a developer carrying member carrying a developer having toner and magnetic particles, and a developer supplied to the developer carrying member. A circulation path that circulates while being agitated, a replenishment means that replenishes at least the magnetic particles to the circulation path, a discharge port that is provided on the circulation path and that overflows and discharges a part of the circulating developer, A rotation shaft rotatably provided in a circulation path facing the discharge port, and a conveyance member provided with a protrusion and a blade formed around the rotation axis, the conveyance member, With respect to the axial direction of the rotating shaft, the protrusion includes a first region including at least a portion facing the discharge port, and a second region adjacent to the first region, and the protrusion formed in the first region. Is the blade portion formed in the second region. The protrusion having a small outer diameter is formed in the first region, where x is a distance in the axial direction of the rotating shaft with respect to an end point on the most upstream side of the circulation path of the first region, and A distance in the axial direction of the rotating shaft between an end point on the most upstream side of the circulation path in one region and an end point on the upstream side in the developer circulation direction of the protrusion formed in the first region is L1. The axial direction of the rotating shaft between the end point on the most upstream side of the circulation path in the first region and the end point on the downstream side in the developer circulation direction of the protrusion formed in the first region. The transport speed of the developer transported in the rotation direction of the transport member of the developer transported by the transport member at the boundary portion where the distance is L2 and enters the first region from the second region is the transport of the outer peripheral surface of the transport member. The value divided by the moving speed in the rotation direction of the member is γ, and the spiral pin of the conveying member is P, and when the rotation direction of the transport member is positive, the outer peripheral point of the blade portion in the cross section of the blade portion of the transport member at the boundary portion entering the first region from the second region And a first straight line passing through the rotation center of the rotation axis of the conveying member and a cross section at a point of distance x in the protruding portion formed in the first area on the developer conveying surface of the protruding portion. If the angle formed by the second straight line passing through the center of the rotation axis and the rotation center of the rotation axis is α (x), (γ−1) in all x where L1 ≦ x ≦ L2. ) × 360 × (x / p) −α (x) ≠ 0.

  According to the above configuration, it is possible to suppress the developer from jumping up and discharging by the protrusions disposed in the region facing the developer discharge port.

FIG. 2 is a cross-sectional explanatory view illustrating a configuration of an image forming apparatus including a developing device according to the present invention. FIG. 3 is a longitudinal sectional view illustrating a configuration of a developing device according to the present invention. It is a cross-sectional explanatory drawing which shows the structure of the developing device which concerns on this invention. FIG. 2 is an explanatory cross-sectional view illustrating a configuration of a developing device according to the present invention. It is sectional explanatory drawing explaining the subject of the image development apparatus of a comparative example. FIG. 4 is an explanatory cross-sectional view illustrating a configuration in the vicinity of a discharge port of the developing device according to the present invention. FIG. 4 is an explanatory cross-sectional view illustrating a configuration in the vicinity of a discharge port of the developing device according to the present invention. FIG. 10 is a cross-sectional explanatory view illustrating another configuration of the developing device according to the present invention. FIG. 10 is an explanatory cross-sectional view illustrating still another configuration of the developing device according to the present invention. FIG. 10 is an explanatory cross-sectional view illustrating still another configuration of the developing device according to the present invention. FIG. 6 is a cross-sectional explanatory view illustrating the behavior of the developer in the vicinity of the discharge port of the developing device according to the present invention. FIG. 6 is a cross-sectional explanatory view illustrating the behavior of the developer in the vicinity of the discharge port of the developing device according to the present invention. It is a figure explaining the conditions for a developer to jump up by a projection part. It is a figure explaining the conditions for a developer to jump up by a projection part. It is a figure explaining the conditions for a developer to jump up by a projection part. It is a figure explaining the conditions for a developer to jump up by a projection part. It is a figure explaining the conditions for a developer to jump up by a projection part. FIG. 2 is an explanatory cross-sectional view illustrating a configuration of a developing device according to the present invention. It is a figure explaining the structure of the developing device which concerns on this invention. It is sectional explanatory drawing explaining the structure of the image development apparatus of a comparative example. It is a figure explaining the structure of the image development apparatus of a comparative example. (A) is a figure explaining the effect of the developing device concerning the present invention. (B) is a figure explaining the effect of the developing device of a comparative example.

  An embodiment of an image forming apparatus provided with a developing device according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a cross-sectional explanatory view of a full-color image forming apparatus employing an electrophotographic system, which is an embodiment of an image forming apparatus having a developing device according to the present invention. The image forming apparatus can be applied to a copying machine, a printer, a recorded image display apparatus, a facsimile apparatus, and the like.

<Image forming apparatus>
In FIG. 1, an image forming apparatus 36 according to this embodiment includes four image forming portions Pa, Pb, Pc, and Pd of yellow, magenta, cyan, and black serving as image forming units. For convenience of explanation, the image forming units Pa, Pb, Pc, and Pd may be represented on the basis of the image forming unit P. The same applies to other image forming process means. Each image forming portion P is a photosensitive drum 1a, 1b, 1c, which is a drum-shaped electrophotographic photosensitive member that rotates in the direction of the arrow (counterclockwise direction) in FIG. 1d.

  Around each photosensitive drum 1, there are chargers 2a, 2b, 2c, 2d as charging means, and laser beam scanners 3a, 3b, 3c, 3d as image exposing means arranged above the photosensitive drum 1 in FIG. Is provided. Further, developing devices 4a, 4b, 4c and 4d are provided as developing means for supplying a developer to the electrostatic latent image carried on the surface of each photosensitive drum 1 to form a toner image. Further, the image forming unit includes primary transfer rollers 6a, 6b, 6c, and 6d serving as primary transfer units, and cleaning devices 19a, 19b, 19c, and 19d serving as cleaning units.

  Each image forming unit P has the same configuration, and the photosensitive drum 1 arranged in each image forming unit P has the same configuration. Therefore, the photosensitive drums 1a, 1b, 1c, and 1d will be representatively described as the photosensitive drum 1. Similarly, the charger 2, the laser beam scanner 3, the developing device 4, the primary transfer roller 6, and the cleaning device 19 disposed in each image forming unit P have the same configuration in each image forming unit P. Therefore, description will be made using the charger 2, the laser beam scanner 3, the developing device 4, the primary transfer roller 6, and the cleaning device 19, respectively.

<Image formation sequence>
Next, an image forming sequence of the entire image forming apparatus 36 will be described. First, the surface of the photosensitive drum 1 is uniformly charged by the charger 2. Next, the photosensitive drum 1 whose surface is uniformly charged is subjected to scanning exposure with a laser beam 37 modulated by an image signal by the laser beam scanner 3.

  The laser beam scanner 3 has a built-in semiconductor laser. This semiconductor laser is controlled in accordance with a document image information signal output from a document reading apparatus having a photoelectric conversion element such as a CCD (Charge Coupled Device) and emits a laser beam 37.

  As a result, the surface potential of the photosensitive drum 1 charged by the charger 2 changes in the image portion, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is reversely developed by the developing device 4 to be a visible image, that is, a toner image. In the present embodiment, the developing device 4 uses a two-component contact developing system that uses a two-component developer obtained by mixing toner and magnetic particles (carrier) as the developer. Further, by performing the image forming process for each image forming portion P, toner images of four colors of yellow, magenta, cyan, and black are formed on the surface of each photosensitive drum 1.

  In the present embodiment, an intermediate transfer belt 5 serving as an intermediate transfer member is disposed below each image forming unit P in FIG. The intermediate transfer belt 5 is suspended by rollers 61, 62, 63, and is movable in the direction of the arrow in FIG.

  The toner image on the surface of the photosensitive drum 1 is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 5 serving as an intermediate transfer member by a primary transfer roller 6 serving as a primary transfer unit. As a result, four color toner images of yellow, magenta, cyan, and black are superimposed on the outer peripheral surface of the intermediate transfer belt 5 to form a full-color image. Further, the toner remaining without being transferred onto the surface of the photosensitive drum 1 is scraped and collected by the cleaning device 19.

  The full-color image primarily transferred onto the outer peripheral surface of the intermediate transfer belt 5 is fed from a feeding cassette 12 by a feeding roller 13 to a recording material 33 such as paper conveyed via a feeding guide 11. Secondary transfer is performed by the action of the secondary transfer roller 10 serving as a next transfer means. The toner remaining on the outer peripheral surface of the intermediate transfer belt 5 without being transferred is scraped and collected by a cleaning device 18 serving as a cleaning means.

  On the other hand, the recording material 33 on which the toner image on the outer peripheral surface of the intermediate transfer belt 5 is secondarily transferred is sent to a fixing device 16 including a heat roller fixing device as a fixing unit, and heated and pressed by the fixing device 16. Then, the toner image is fixed on the recording material 33. Thereafter, the sheet is discharged onto the discharge tray 17.

  In this embodiment, the photosensitive drum 1 that is a commonly used drum-shaped organic photosensitive member is used as the image carrier. In addition, an inorganic photoreceptor such as an amorphous silicon photoreceptor can also be used. It is also possible to use a belt-like photoreceptor. The charging method, transfer method, cleaning method, and fixing method need not be limited to the present embodiment.

<Developing device>
Next, the configuration and operation of the developing device 4 will be described with reference to FIGS. 2 and 3 are vertical and horizontal cross-sectional explanatory views of the developing device 4 according to the present embodiment. As shown in FIGS. 2 and 3, the developing device 4 of the present embodiment includes a developing container 22 that contains a two-component developer having toner and magnetic particles (carrier). In the developing container 22, a two-component developer containing toner and magnetic particles (carrier) is accommodated as a developer. In addition, the developing container 22 includes a developing sleeve 28 serving as a developer carrier that is rotatably disposed facing the opening 43 of the developing container 22. Further, a regulation blade 29 is provided as a spike cutting member that regulates the spikes of the developer carried on the surface of the developing sleeve 28.

  As shown in FIG. 3, a partition wall 27 having a substantially central portion extending in a direction perpendicular to the paper surface of FIG. A partition wall 27 divides the developing chamber 23 and the agitating chamber 24 vertically in FIGS. At both ends of the partition wall 27, communication portions 14 and 15 each having an opening are provided. The developing chamber 23 and the stirring chamber 24 are configured as a circulation path through which the developer supplied to the developing sleeve 28 via the communication portions 14 and 15 circulates while being stirred. The developer is accommodated in the developing chamber 23 and the stirring chamber 24.

  In the developing chamber 23 and the agitating chamber 24, first and second conveying screws 25 and 26, which are conveying members for conveying the developer, are arranged, respectively. The first conveying screw 25 is disposed substantially parallel to the bottom of the developing chamber 23 along the axial direction of the developing sleeve 28. The first conveying screw 25 rotates in the direction of the arrow in FIG. 2 (clockwise direction) to supply the developer in the developing chamber 23 to the developing sleeve 28, and at the same time, the axis of the screw shaft 51 that serves as the rotation axis of the developer. Convey in one direction along the direction.

  On the circulation path of the developing chamber 23 constituting the developer circulation path, there is provided a discharge port 40 through which a part of the circulated developer overflows and is discharged out of the circulation path. The screw shaft 51 is rotatably provided in a circulation path facing the discharge port 40 provided in the developing chamber 23.

  The second conveying screw 26 is disposed substantially parallel to the first conveying screw 25 at the bottom in the stirring chamber 24. Then, the developer after being rotated and rotated in the direction opposite to the first conveying screw 25 (counterclockwise direction) is collected. Further, the developer in the stirring chamber 24 is transported in the direction opposite to the first transport screw 25.

  As described above, the developer is conveyed between the developing chamber 23 and the agitating chamber 24 through the communicating portions 14 and 15 which are the openings at both ends of the partition wall 27 by the conveyance by the rotation of the first and second conveying screws 25 and 26. Circulated.

  In the first and second conveying screws 25 and 26, screw blades 51a and 52a having an outer diameter of 18 mm are spirally wound around screw shafts 51 and 52 having an outer diameter of 6 mm. As shown in FIG. 4, the screw pitches 51 in the direction of the screw shafts 51 and 52 of the screw blades 51a and 52a are both 40 mm.

<Configuration of drive control system>
Next, the configuration of the drive control system of the developing device 4 will be described with reference to FIG. The developing sleeve 28 is rotationally driven by a motor 7 serving as driving means. The first and second conveying screws 25 and 26 are rotationally driven by a motor 8 serving as driving means. In this embodiment, the motors 7 and 8 are both direct current (DC) motors. In the present embodiment, the motors 7 and 8 are driven and controlled by the control unit 20 serving as control means.

  The rotation speed of the motor 7 in a steady state during image formation is set to 300 rpm (rotation per minute), and the rotation speed of the motor 8 is set to 700 rpm. In this embodiment, the motors 7 and 8 are directly connected to the developing sleeve 28 and the first conveying screw 25, respectively. Further, the first conveying screw 25 and the second conveying screw 26 are connected and rotated by a gear train (not shown) having a gear ratio of 1: 1.07.

  In the present embodiment, there is an opening 43 at a position corresponding to the developing region of the developing container 22 facing the photosensitive drum 1, and the developing sleeve 28 is partially exposed in the opening 43 toward the photosensitive drum 1. It is arrange | positioned so that rotation is possible. The developing sleeve 28 has an outer diameter of 20 mm and is driven to rotate at a rotation speed of 300 rpm. The outer diameter of the photosensitive drum 1 is 30 mm, and the rotation speed is 120 rpm.

  The closest region between the developing sleeve 28 and the photosensitive drum 1 is set to a separation distance of about 400 μm. As a result, the developer conveyed to the developing portion where the developing sleeve 28 and the photosensitive drum 1 face each other is set so that the development can be performed in a state where the developer is in contact with the photosensitive drum 1.

  The developing sleeve 28 of the present embodiment is made of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 28m serving as a magnetic field generating means is installed in a non-rotating state therein. The developing sleeve 28 rotates in the direction of the arrow in FIG. 2 (counterclockwise direction) during development. Then, the two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the regulating blade 29 is carried. This is conveyed to a developing area facing the photosensitive drum 1, and a developer is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 1 to develop the electrostatic latent image as a toner image.

The regulating blade 29 includes a nonmagnetic member 29a formed of a plate-like aluminum or the like extending along the longitudinal axis of the developing sleeve 28, and a magnetic member 29b such as an iron material. Further, by adjusting the gap between the regulating blade 29 and the surface of the developing sleeve 28, the amount of developer conveyed to the developing region is adjusted. In the present embodiment, the amount of developer coat per unit area on the surface of the developing sleeve 28 is regulated to 30 mg / cm ² by the regulating blade 29. The gap between the regulating blade 29 and the developing sleeve 28 is appropriately set in the range of 200 μm to 1000 μm, preferably 300 μm to 700 μm. In the present embodiment, the gap between the regulating blade 29 and the developing sleeve 28 is set to 400 μm.

<Two-component developer>
Next, a two-component developer containing toner and magnetic particles (carrier) used in this embodiment will be described. The toner includes colored resin particles containing a binder resin, a colorant, and other additives as necessary, and colored particles to which an external additive such as colloidal silica fine powder is externally added. Yes. The toner is a negatively chargeable polyester resin, and the volume average particle size is preferably 4 μm or more and 10 μm or less. More preferably, it is 8 μm or less.

As the magnetic particles (carriers), for example, surface oxidation or unoxidized metals such as iron, nickel, cobalt, manganese, chromium, rare earth, alloys thereof, oxide ferrite, etc. can be suitably used. The method for producing these magnetic particles is not particularly limited. The average particle diameter of the magnetic particles (carrier) is 20 μm to 60 μm, preferably 30 μm to 50 μm, and the resistivity of the magnetic particles (carrier) is 1 × 10 ⁷ Ωcm or more, preferably 1 × 10 ⁸ Ωcm or more. In the present embodiment, magnetic particles (carrier) having a resistivity of 1 × 10 ⁸ Ωcm are used.

<Developer replenishment method>
Next, a developer replenishing method according to this embodiment will be described with reference to FIGS. As shown in FIGS. 2 and 3, a hopper 31 serving as a replenishing means for accommodating a replenishing two-component developer in which toner and magnetic particles (carriers) are mixed is disposed at the upper portion of the developing device 4. A hopper 31 serving as a replenishing unit replenishes at least magnetic particles (carriers) to the developing chamber 23 serving as a circulation path.

  The hopper 31 includes a screw-like supply screw 32 serving as a conveying member at the lower portion, and one end of the supply screw 32 extends to the position of the supply port 30 provided at the right end of the developing device 4 in FIG.

  The toner consumed by the image formation passes through the supply port 30 from the hopper 31 and is supplied into the developing container 22 by the rotational force of the supply screw 32 and the gravity of the developer. In this way, the replenishment developer is supplied from the hopper 31 to the developing device 4. The supply amount of the supply developer is roughly determined by the rotation speed of the supply screw 32. The number of rotations of the replenishing screw 32 is determined by the control unit 20 that also serves as a toner replenishing amount control unit that controls the motor 9 that is a driving source for rotationally driving the replenishing screw 32.

  As a method for controlling the toner replenishment amount, the toner density of the two-component developer is detected optically or magnetically, or the reference latent image on the surface of the photosensitive drum 1 is developed and the density of the toner image is adjusted. Various methods such as a detection method can be applied.

<Developer discharge method>
Next, a developer discharging method in the present embodiment will be described with reference to FIG. A discharge port 40 constituting developer discharge means is provided outside the installation area of the development sleeve 28 on the downstream side of the development chamber 23 in the developer circulation direction. The developer is discharged from the discharge port 40.

  When the developer in the developing device 4 is increased by the developer replenishment process, the developer is discharged so as to overflow from the discharge port 40 according to the increased amount. The position of the discharge port 40 is formed upstream of the position of the developer supply port 30 in the developer transport direction. This is to prevent new developer replenished from the replenishing port 30 from being immediately discharged from the discharge port 40.

  Moreover, FIG. 6 is a figure explaining the part which opposes the discharge port 40 of the 1st conveying screw 25 in this embodiment. In the present embodiment, a small-diameter rib member 41 serving as a protruding portion and a screw blade 51a serving as a blade portion are provided around the screw shaft 51 of the first conveying screw 25. As shown in FIG. 6, the first conveying screw 25 includes, in the axial direction of the screw shaft 51, a first region including at least a portion facing the discharge port 40 and a second region adjacent to the first region. Have.

  In the present embodiment, the screw blade 51a in the first region, which is a portion facing the discharge port 40, is omitted. Further, a small-diameter rib member 41 is provided at that portion for exciting the developer so as to be parallel to the axial direction of the screw shaft 51. The rib member 41 formed in the first region shown in FIG. 6 has an outer diameter smaller than that of the screw blade 51a formed in the second region.

  In the present embodiment, as shown in FIG. 6, the axial length of the screw shaft 51 in the first region in which the screw blades 51a of the first conveying screw 25 are omitted is 14 mm. Moreover, the length of the axial direction of the screw shaft 51 of the discharge port 40 is 10 mm. Moreover, the length of the axial direction of the screw shaft 51 of the rib member 41 which becomes a protrusion part is 8 mm.

  The center in the axial direction of the screw shaft 51 of the first region in which the screw blade 51a is omitted, the center in the axial direction of the screw shaft 51 of the discharge port 40, and the center of the rib member 41 in the axial direction of the screw shaft 51 are as follows: It is as follows. All the screw shafts 51 are arranged at the same position in the axial direction.

  Moreover, as shown in FIG. 7, the cross-sectional shape of the rib member 41 of this embodiment is comprised by substantially ellipse shape. The cross section of the rib member 41 gradually narrows from the root of the screw shaft 51 to the tip. As shown in FIG. 7, the outer diameter radius R of the screw shaft 51 of the first conveying screw 25 is 3 mm. The height h of the rib member 41 from the rotation center o of the screw shaft 51 is 5 mm. The height h (= 5 mm) of the rib member 41 from the rotation center o of the screw shaft 51 is smaller than the height A (= 18 mm) of the screw blade 51a from the rotation center o of the screw shaft 51 shown in FIG.

  As shown in FIG. 7, the installation height H from the bottom surface of the developing container 22 at the rotation center o of the screw shaft 51 of the first conveying screw 25 is 10 mm.

  As shown in FIG. 7, the rib member 41 has two long shaft portions 41 a and 41 b that protrude in opposite directions from the screw shaft 51. The distal end portion of the rib member 41 is configured to have semicircular portions 41c and 41d having a radius r of 0.5 mm. The rib member 41 includes tangential portions 41e and 41f that are in contact with the outer peripheral surface 51c of the screw shaft 51 and the semicircular portions 41c and 41d at the tip portions. The long shaft portions 41a and 41b of the rib member 41 are line symmetric with respect to the straight lines Ma and Mb passing through the rotation center o of the screw shaft 51 and the vertices of the semicircular portions 41c and 41d at the tip portions, respectively. The angle formed by the straight line Ma and the straight line Mb is 180 °.

  The rib member 41 is assumed to be the same with respect to the axial direction of the screw shaft 51 with respect to the installation phase with respect to the first conveying screw 25. With such a configuration, the rib member 41 oscillates the developer in the portion facing the discharge port 40 as the first conveying screw 25 rotates, so that the developer is unraveled and loosened. (So) and eliminate the local bulge of the developer surface. As a result, the developer is prevented from overflowing from the discharge port 40 at a time, and stable developer discharge is realized.

  Generally, if the average angle formed by the conveying surface 41g for conveying the developer of the rib member 41 formed in the first region and the axial direction of the screw shaft 51 of the first conveying screw 25 is as follows: The effect of leveling the developer can be obtained. It is set to be smaller than the average angle formed by the conveying surface 51b for conveying the developer of the screw blade 51a formed in the second region adjacent to the first region and the axial direction of the screw shaft 51. Then, the effect of leveling the developer can be obtained.

  Therefore, in the present embodiment, as shown in FIG. 7, the conveying surface 41g for conveying the developer of the rib member 41 and the axial direction of the screw shaft 51 of the first conveying screw 25 are set in parallel. The average angle formed by them is 0 °. Further, as shown in FIG. 8, the average angle formed by the conveying surface 51b for conveying the developer of the screw blade 51a and the axial direction of the screw shaft 51 is approximately 60 °.

  For example, as illustrated in FIG. 8, the rib member 41 has a rectangular cross section along the axial direction of the screw shaft 51, or as illustrated in FIG. 9, the rib member 41 has a rectangular cross section and the axial direction of the screw shaft 51. May be provided with a slight angle to the angle.

  At this time, the inclination angle of the rib member 41 with respect to the axial direction of the screw shaft 51 is excessively increased. Then, the average angle formed by the conveying surface 41g for conveying the developer of the rib member 41 formed in the first region shown in FIG. 6 and the axial direction of the screw shaft 51 of the first conveying screw 25 is as follows. Street. The developer becomes larger than the average angle formed by the conveying surface 51b of the screw blade 51a formed in the second region adjacent to the first region and the axial direction of the screw shaft 51. The effect of leveling may not be obtained.

  In the case where the leveling effect of the developer is not assumed, as shown in FIG. 6, the rib member 41 is provided at least outside the screw blade 51a in the second region adjacent to the first region where the rib member 41 is provided. It is simply configured with a smaller diameter than the diameter. The rib member 41 shown in FIG. 10 is configured by a part of a spiral blade portion having a smaller diameter than the outer diameter of the screw blade 51a in the second region adjacent to the first region where the rib member 41 is provided. is there.

  However, when such a rib member 41 is installed, the following problems occur depending on the installation phase in the rotation direction of the first conveying screw 25 as shown in FIG. Even if the developer is not jumped up by the rib member 41 itself, the developer wound up by the downstream end portion U of the screw blade 51a in the second region adjacent to the upstream side of the first region facing the discharge port 40 is not removed. Colliding with the rib member 41. As a result, the developer is splashed up and overflows from the discharge port 40.

  FIG. 11 is a view of the vicinity of the discharge port 40 as viewed from above. As shown in FIG. 11, the developer rides on the conveyance surface 51b of the screw blade 51a and is conveyed downstream in the developer circulation direction (right side in FIG. 11). The developer reaches a boundary line Lc which is a boundary portion where the developer enters the first region where the screw blade 51a is omitted from the second region where the screw blade 51a is provided. Then, the developer receives a force in the rotational direction of the first conveying screw 25 by the downstream end portion U of the screw blade 51a of the boundary line Lc, and the course is slightly changed as shown in FIG.

  Here, the distances L1 and L2 shown in FIGS. 11 and 12 are as follows. The axial direction of the screw shaft 51 between the boundary line Lc which is the end point on the most upstream side of the circulation path of the first region and the upstream end 41h or the downstream end 41i of the rib member 41 (see FIGS. 11 and 11) 12 horizontal distances). The upstream end 41h is an end point on the upstream side (left side in FIGS. 11 and 12) of the rib member 41 formed in the first region in the developer circulation direction. The downstream end 41i is an end point of the rib member 41 on the downstream side in the developer circulation direction (the right side in FIGS. 11 and 12).

  That is, the distances L1 and L2 are determined from the boundary line Lc passing through the downstream end portion U of the screw blade 51a in the second region adjacent to the upstream side of the first region facing the discharge port 40, and the upstream end portion 41h of the rib member 41. And the distance in the axial direction of the screw shaft 51 at the downstream end 41i.

  The speed component given to the rotational direction component of the screw blade 51a by the downstream end portion U of the screw blade 51a of the screw blade 51a varies depending on the case. The maximum speed is the same as the speed of the downstream end portion U of the screw blade 51a in the rotational direction of the screw blade 51a. In addition, the minimum is zero. In other words, the downstream end portion U of the screw blade 51a is not subjected to any force in the rotational direction of the screw blade 51a, and passes through the screw shaft 51 in the axial direction as it is.

  That is, when the rotational speed of the first conveying screw 25 is ωr [rps (rotations per second)] and the rotational speed that the developer is given by the downstream end portion U of the screw blade 51a is ωd, the following equation 1 is obtained. It becomes the relationship shown.

[Equation 1]
0 ≦ ωd ≦ ωr

  On the other hand, the developer receives a force from the downstream end portion U of the screw blade 51a and enters the omitted portion of the screw blade 51a. The moving speed of the developer in the axial direction of the screw shaft 51 at that time is the moving speed of the screw blade 51a regardless of the speed component given to the rotational direction component of the screw blade 51a by the downstream end portion U of the screw blade 51a. Is almost equivalent.

  Therefore, the time t (x) required for the developer to jump from the downstream end portion U of the screw blade 51a to reach the distance x in the axial direction of the screw shaft 51 with respect to the boundary line Lc is as follows. It is as follows. The boundary line Lc is a boundary line with the abbreviated portion of the screw blade 51a that is an end point on the most upstream side of the circulation path in the first region. The helical pitch of the screw blades 51a of the first conveying screw 25 is set to p, and the rotational speed ωr of the first conveying screw 25 is used.

[Equation 2]
t (x) = x / (p × ωr)

  Therefore, the rotation angle θs of the first conveying screw 25 at this time and the angle θd at which the developer sprung up by the downstream end portion U of the screw blade 51a rotates are as follows. Using the formula 2 and the rotational speed ωd at which the developer is provided by the downstream end portion U of the screw blade 51a, the following formula 3 is used.

[Equation 3]
θs = 360 × t (x) × ωr = 360 × (x / p)
θd = 360 × t (x) × ωd = 360 × (xωd / pωr) = (ωd / ωr) × θs

  The horizontal axis in FIG. 13 indicates the distance x in the axial direction of the screw shaft 51 from the boundary line Lc with the omitted portion of the screw blade 51a. In addition, the vertical axis in FIG. 13 indicates the rotation angle θ from when the developer is splashed up by the downstream end portion U of the screw blade 51a until it reaches the position corresponding to the distance x. The developer bounced up by the downstream end portion U of the screw blade 51a reaches a position corresponding to the distance x in the axial direction of the screw shaft 51 from the boundary line Lc. The rotation angle θs of the first conveying screw 25 at that time and the angle θd at which the developer bounced up by the downstream end portion U of the screw blade 51a rotates are in a graph as shown in FIG.

  Lines a, b, and c shown in FIG. 13 show examples of the angle θd at which the developer sprung up by the downstream end portion U of the screw blade 51a rotates. The straight lines a, b, and c are examples when the rotational component values of the first conveying screw 25 received by the developer from the downstream end portion U of the screw blade 51a are different.

  (Ωd / ωr) shown in the final term of Equation 3 is 1 or less from the relationship of Equation 1. Therefore, the angle θd at which the developer bounced up by the downstream end portion U of the screw blade 51a rotates is equal to or smaller than the rotation angle θs of the first conveying screw 25. Therefore, the angle θd at which the developer bounced up by the downstream end portion U of the screw blade 51a rotates is the straight line of the rotation angle θs of the first conveying screw 25 shown in FIG. 13 and the value x shown in FIG. Exists in a region surrounded by a horizontal axis where 0 is 0 or more.

  In the graph shown in FIG. 13, the origin O is a point where the developer is splashed by the downstream end portion U of the screw blade 51a of the screw blade 51a. Furthermore, as shown in FIG. 14, for example, the outer peripheral point U1 of the screw blade 51a at the downstream end portion U of the screw blade 51a in the second region adjacent to the upstream side of the first region, and the rotation center o of the screw shaft 51 A straight line N is set. A rib member 41 is installed at a phase angle α (x) with the rotational direction of the first conveying screw 25 as a positive direction from the first straight line N around the rotational center o of the screw shaft 51.

  Then, after the developer is sprung up by the downstream end portion U of the screw blade 51a, the rib member 41 rotates, and the developer reaches a position corresponding to the distance x in the axial direction of the screw shaft 51 from the boundary line Lc. To do. The arrival angle θr of the rib member 41 at that time is expressed by the following equation (4) as shown by a one-dot chain line in FIG.

  Note that the arrival angle θr is an angle with the origin O as a point where the developer is sprung up by the downstream end portion U of the screw blade 51a of the screw blade 51a. On the other hand, the rotation angles θs and θd shown in FIGS. 15 and 16 are the rotation angles of the screw blade 51a after the developer is sprung up by the downstream end portion U of the screw blade 51a.

  As shown in FIG. 13, when the developer is splashed by the downstream end portion U of the screw blade 51a and the origin O is taken as a reference, the first conveyance when the developer is at a position corresponding to the distance x. The arrival angle of the screw 25 and the developer coincides with the rotation angles θs and θd. As shown in FIG. 14, the rotation angle of the first conveying screw 25 is positive, and the phase angle α (x) at which the rib member 41 is installed is an angle in the negative rotation direction from the origin O.

  Here, in the following formula 4, the rotation angle of the first conveying screw 25 is positive, and the phase angle at which the rib member 41 is installed is represented by α (x) as a function of x. The reason is that the phase angle at which the rib member 41 is installed generally depends on the position in the axial direction of the screw shaft 51 (the position corresponding to the distance x in the axial direction of the screw shaft 51 from the boundary line Lc). This is also possible.

[Equation 4]
θr = θs + α (x)

  FIGS. 14 to 16 show this using cross-sectional views of the first conveying screw 25. FIG. 14 to 16 show the relationship between the developer and the first conveying screw 25 in the case where the developer bounced up by the downstream end portion U of the screw blade 51a shown in FIG. Indicates.

  FIG. 14 is a cross-sectional view at the moment (x = 0) when the developer receives a force from the downstream end portion U of the screw blade 51a at the boundary line Lc of the omitted portion of the screw blade 51a. 15 and 16 are cross-sectional views at positions corresponding to the distance x (= x1, x2) in the axial direction of the screw shaft 51 with reference to the boundary line Lc of the omitted portion of the screw blade 51a. 14 to 16, for the sake of convenience, the downstream end portion U of the screw blade 51a in the second region adjacent to the upstream side of the first region (hereinafter simply referred to as “the downstream end portion U of the screw blade 51a”). The point (phase) at which the developer receives force is indicated as upward. Further, “Origin point O” corresponds to the origin point O in FIG.

  The speed at which the developer advances in the x direction indicated by the horizontal axis in FIG. After the developer is splashed up by the downstream end portion U of the screw blade 51a, the developer advances in the axial direction of the screw shaft 51. Further, the developer rotates together with the first conveying screw 25. FIG. 14 to FIG. 16 represent such a movement of the developer over time.

  As shown in FIG. 14, at the moment when the developer receives a force from the downstream end portion U of the screw blade 51a at the boundary line Lc of the omitted portion of the screw blade 51a, the following occurs. The position where the developer is present is a distance x = 0 in the axial direction of the screw shaft 51 of the developer from the boundary line Lc, and t (x) = 0 from the above equation (2). The rotation angle of the developer and the first conveying screw 25 at that time is 0 ° as shown in FIG. 14, and the phase angle α (x) of the rib member 41 is as shown in FIG.

  In FIG. 15, the developer bounced up by the downstream end portion U of the screw blade 51a is the distance of the developer in the axial direction of the screw shaft 51 from the boundary line Lc at time t (x1) from the equation (2). x is in the position of x1. The angles of the developer, the first conveying screw 25, and the rib member 41 at that time (position of distance x1) are as shown in FIG.

  Further, as time elapses, the distance x in the axial direction of the screw shaft 51 of the developer from the boundary line Lc at the time t (x2) from the equation (2) becomes the position x2. The angles of the developer, the first conveying screw 25, and the rib member 41 at that time (position of distance x2) are as shown in FIG.

  As can be seen from FIGS. 13 to 16, the rib member 41 prevents the developer splashed and wound up at the downstream end portion U of the screw blade 51a from being further splashed. For this purpose, the developer sprung up by the downstream end portion U of the screw blade 51a should not be caught up by the rib member 41 while passing through the region where the rib member 41 is present.

  That is, all of L1 ≦ x ≦ L2 shown in FIG. 13 using distances L1 and L2 in the axial direction of the screw shaft 51 from the boundary line Lc between the upstream end portion 41h and the downstream end portion 41i of the rib member 41 shown in FIG. In the case of x, the relationship shown by the following formula 5 may be used.

[Equation 5]
θd−θr = (ωd / ωr−1) × 360 × (x / p) −α (x) ≠ 0

  Specifically, the straight lines a and b shown in FIG. 13 do not intersect with the straight line θr in all x of L1 ≦ x ≦ L2 on the x axis shown by the horizontal axis in FIG. The conditions shown are met. However, since the straight line c shown in FIG. 13 intersects the straight line θr at all x of L1 ≦ x ≦ L2 on the x axis shown by the horizontal axis in FIG. .

  Accordingly, in the case indicated by the straight line c shown in FIG. 13, the angle θd at which the developer sprung up by the downstream end portion U of the screw blade 51a rotates is as follows. The developer bounced up by the downstream end portion U of the screw blade 51a passes through the region where the rib member 41 is present. In the meantime, there is a high possibility that the developer caught up by the rib member 41 and spun up at the downstream end portion U of the screw blade 51a will be further spun up by the rib member 41 and overflow from the discharge port 40.

  Further, the rib member 41 actually has a predetermined thickness as shown in FIG. 17 instead of the long and thin cross-sectional shape schematically shown in FIGS. The developer receives a force from the conveyance surface 41g on the upstream side in the rotation direction of the rib member 41 shown in FIG. Therefore, only the conveying surface 41g of the rib member 41 needs to be considered. The developer collides with the conveying surface 41g of the rib member 41 and receives a force. Even if the developer collides with a point close to the base of the rib member 41, the developer is developed because the distance from the rotation center o of the screw shaft 51 is short. It does not receive the force that the agent leaks from the discharge port 40.

  According to the study by the present inventor, the higher the tip side of the rib member 41 is, the higher the speed when the developer is splashed by the force received by collision. In general, the following is considered with reference to the outer peripheral surface 51c (rotary shaft outer peripheral surface) of the screw shaft 51, which is the rotational axis of the rib member 41 shown in FIG.

  As shown in FIG. 17, the outer diameter radius of the screw shaft 51 from the height h of the apex of the outer peripheral surface 41j of the semicircular portions 41c, 41d that is the highest point of the rib member 41 from the rotation center o of the screw shaft 51. Consider the distance B minus R (= h−R). Then, only the conveying surface 41g of the rib member 41 at a height position of about 8/10 (about 80%) or more of the distance B (= h−R) needs to be considered.

  The distance B obtained by subtracting the outer radius R of the screw shaft 51 from the height h of the apex of the outer circumferential surface 41j of the semicircular portions 41c and 41d, which is the highest point of the rib member 41, with respect to the outer circumferential surface 51c of the screw shaft 51. Consider (= h−R). Then, the developer collides with the conveyance surface 41g of the rib member 41 at a height position lower than about 8/10 (about 80%) of the distance B (= h−R). In this case, the energy is small, and in addition, a lot of developer is surrounded by the outer periphery of the collided developer. For this reason, the developer does not receive energy that leaks from the discharge port 40, and the developer is prevented from being discharged from the discharge port 40.

  After the developer collides with the rib member 41, the developer does not leak from the discharge port 40. For this purpose, the following is performed with reference to the outer peripheral surface 51c of the screw shaft 51 on the conveyance surface 41g on the upstream side in the rotation direction of the rib member 41 shown in FIG. Considering a distance B (= h−R) obtained by subtracting the outer diameter radius R of the screw shaft 51 from the height h of the apex of the outer peripheral surface 41j of the semicircular portions 41c and 41d, which is the highest point of the rib member 41. . Then, the developer collides with the transport surface 41g on the semicircular portion 41c, 41d side of the rib member 41 from the point Q of the height h1 of about 8/10 (about 80%) of the distance B (= h−R). It is necessary to prevent that.

  That is, at least in the cross section at the point of the distance x in the rib member 41 formed in the first region, the second straight line K has a predetermined height on the developer conveying surface 41g (on the conveying surface) of the rib member 41. The point Q shown in FIG. Further, it passes through the rotation center o of the screw shaft 51 of the first conveying screw 25. It is sufficient that the second straight line K does not catch up with the developer splashed by the downstream end portion U of the screw blade 51a.

  For this reason, in the cross section of the screw blade 51a of the first conveying screw 25 at the boundary line Lc that is a boundary portion entering from the second region to the first region when the rotation direction of the first conveying screw 25 is positive, It is as follows. The angle formed between the first straight line N passing through the outer peripheral point U1 of the screw blade 51a, the rotation center o of the screw shaft 51, and the second straight line K is a phase angle α ( x).

  As described above, the developer amount in the developer container 22 increases and the developer surface rises. Then, a distance B (= h−R) obtained by subtracting the outer diameter radius R of the screw shaft 51 from the height h of the apex of the rib member 41 on the conveying surface 41g on the upstream side in the rotation direction of the rib member 41 shown in FIG. Consider. Then, the developer collides with the transport surface 41g on the semicircular portion 41c, 41d side of the rib member 41 from the point Q of the height h1 of about 8/10 (about 80%) of the distance B (= h−R). To do. Even in this case, the developer surface is sufficiently high, and there is plenty of developer around the developer colliding with the conveying surface 41g of the rib member 41. In that case, there is little possibility that the developer bounced up at the downstream end portion U of the screw blade 51a is further bounced up by the rib member 41 and overflows from the discharge port 40.

  Further, the rotational speed ωd to which the developer is given by the downstream end portion U of the screw blade 51a is as shown in the above-described equation (1). By using a known high-speed camera (not shown), the rotational speed ωd at which the developer is actually applied by the downstream end portion U of the screw blade 51a can be obtained.

<Measurement of rotational speed at which developer is applied by downstream end of blade>
First, the developing container 22 is fixed to a jig (not shown) that can be driven in the same manner as the image forming apparatus 36 shown in FIG. 1, and is discharged so that the rib member 41 and the downstream end portion U of the screw blade 51a can be seen from the discharge port 40. A high-speed camera (not shown) is installed at a position substantially perpendicular to the outlet 40. If the whole cannot be seen from the discharge port 40, the periphery of the discharge port 40 is appropriately cut and removed as necessary. In this embodiment, the periphery of the discharge port 40 was removed by cutting 10 mm into a U-shape.

  Next, a desired amount of developer is put in the developing container 22 and driven with the same setting as the image forming apparatus 36 shown in FIG. Thereafter, shooting is performed at a frame rate (a value indicating how many frames (video) are processed per unit time in a moving image) such that the developer lump can be recognized well.

  In this embodiment, as a high-speed camera, an image was taken for 1 second at 2000 fps (frames per second) using a resolution of 1024 × 1024. Also, if the frame rate is increased, the image becomes darker, so a light source is used as necessary. In this embodiment, a xenon lamp light source manufactured by Tokina Co., Ltd. was used.

  Next, it is determined how many pixels the developer moves in the rotation direction on the image for each frame of the photographed video. It is not necessary to compare every frame, and the comparison may be performed every 100 frames as long as the developer can be followed. In this way, the developer movement amount at the moment when the spring blade 51a jumps up at the downstream end portion U is obtained. The follow-up of the developer may be performed visually, or may be followed by light and shade obtained by converting the density of the image.

  Next, the amount of movement in the rotational direction of the first conveying screw 25 including the downstream end portion U of the screw blade 51a is also obtained. Then, the amount of movement of the first conveying screw 25 and the movement of the developer that determines how many pixels the developer moves in the rotation direction on the image with respect to each frame of the image taken by the high-speed camera described above The ratio γ with the quantity is obtained. At this time, it is desirable that the developer photographed by the high-speed camera and the first conveying screw 25 are photographed simultaneously.

  γ is as follows at the boundary line Lc which is a boundary part entering the first region from the second region. The moving speed of the developer conveyed by the screw blade 51a of the first conveying screw 25 in the rotational direction of the screw blade 51a is divided by the moving speed of the outer peripheral surface 51d of the screw blade 51a in the rotational direction of the screw blade 51a. Value.

  When determining the amount of movement of the developer and the first conveying screw 25 in the rotational direction, the amount of movement at a point that substantially crosses the straight line connecting the lens of the high-speed camera and the rotation center o of the screw shaft 51 is calculated. Ask. At the point that clearly deviates from the point that substantially crosses the straight line connecting the lens of the high-speed camera and the rotational center o of the screw shaft 51, the amount of movement of the developer and the first conveying screw 25 in the rotational direction is correctly set. There are cases where it cannot be determined.

  When the amount of movement in the rotational direction of the developer splashed up at the downstream end portion U of the screw blade 51a is distributed and varies, the average value is the rotation of the developer at the downstream end portion U of the screw blade 51a. The amount of movement in the direction.

  In the present embodiment, the FASTCAM SA4 manufactured by Photolon was used as a high-speed camera. The amount of movement of the developer in the rotation direction obtained by calculating how many pixels the developer has moved in the rotation direction on the image with respect to each frame of the image taken by the high-speed camera is determined by the rotation direction of the first conveying screw 25. The ratio γ divided by the amount of movement was about 0.57. The ratio γ, the rotational speed ωd given by the downstream end U of the screw blade 51a in the portion where the screw blade in the first region where the developer faces the discharge port 40 is omitted, and the first conveying screw If the rotational speed ωr is used, it is expressed by the following equation (6).

[Equation 6]
γ = ωd / ωr

  Thus, the following equation (7) is expressed using the above equations (5) and (6).

[Equation 7]
θd−θr = (ωd / ωr−1) × 360 × (x / p) −α (x) = (γ−1) × 360 × (x / p) −α (x)

  In the present embodiment, the distances L1 and L2 in the axial direction of the screw shaft 51 from the boundary line Lc between the upstream end 41h and the downstream end 41i of the rib member 41 shown in FIG. 11 are the distance L1 of 4 mm and the distance L2 of 12 mm. As shown in FIG. 18, the phase angles αa (x) and αb (x) at which the two long shaft portions 41a and 41b of the rib member 41 are installed are the same as those of the screw shaft 51 when the boundary line Lc is used as a reference. It does not depend on the axial distance x.

  The two long shaft portions 41a and 41b are always installed with a phase angle of αa (x) = + 9.86 ° and αb (x) = − 170.14 ° with respect to the downstream end portion U of the screw blade 51a. ing. The center line of the rib member 41 in the cross-sectional view shown in FIG. 18 and the center line of the downstream end portion U of the screw blade 51a overlap on the first straight line N.

  Thereby, the rotation angle of the first conveying screw 25 is set to θs. Let θd be the angle at which the developer bounced up by the downstream end U of the screw blade 51a rotates. The rib member 41 rotates after the developer is splashed up by the downstream end portion U of the screw blade 51a. The arrival angles of the two long shaft portions 41a and 41b of the rib member 41 when the developer reaches a position corresponding to the distance x in the axial direction of the screw shaft 51 from the boundary line Lc are θra and θrb, respectively. To do. Then, θra and θrb are as shown in FIG. The relationship shown in the following formula 9 is satisfied for all x in the range shown in the following formula 8.

[Equation 8]
L1 = 4 ≦ x ≦ L2 = 12

[Equation 9]
θd−θra = (γ−1) × 360 × (x / p) −αa (x) = 0.43 × 360 × (x / 40) −9.86 ≠ 0
And θd−θrb = (γ−1) × 360 × (x / p) −αb (x) = 0.43 × 360 × (x / 40) + 17.014 ≠ 0

  As shown in FIG. 19, the long shaft portions 41a and 41b of the rib member 41 reach a position where the developer corresponds to a distance x in the axial direction of the screw shaft 51 from the boundary line Lc. The straight lines indicating the arrival angles θra and θrb of the two long shaft portions 41a and 41b of the rib member 41 at that time are as follows. Within the range shown in the equation (8), the developer bounced up by the downstream end portion U of the screw blade 51a does not intersect with the straight line of the rotation angle θd.

  As a result, the developer splashed up by the downstream end portion U of the screw blade 51a is caught up by the long shaft portions 41a and 41b of the rib member 41 while passing through the region where the long shaft portions 41a and 41b of the rib member 41 are present. It will not be. Therefore, the developer that has been splashed and wound up at the downstream end portion U of the screw blade 51a is not further splashed by the long shaft portions 41a and 41b of the rib member 41. As a result, the developer does not leak from the discharge port 40.

  On the other hand, FIG. 20 shows a comparative example. In the comparative example shown in FIG. 20, the distances L1 and L2 in the axial direction of the screw shaft 51 from the boundary line Lc between the upstream end 41h and the downstream end 41i of the rib member 41 are the distance L1 of 4 mm and the distance L2 of 12 mm. It is.

  The phase angles αa (x) and αb (x) at which the two long shaft portions 41a and 41b of the rib member 41 are installed are as follows. Two long shaft portions 41a and 41b are installed with a phase angle αa (x) = + 140.86 ° and a phase angle αb (x) = − 30.14 ° with respect to the downstream end portion U of the screw blade 51a. ing.

  At this time, the rotation angle θs of the first conveying screw 25 and the angle at which the developer sprung up by the downstream end portion U of the screw blade 51a rotates is θd. The rib member 41 rotates after the developer is splashed up by the downstream end portion U of the screw blade 51a. The arrival angles of the two long shaft portions 41a and 41b of the rib member 41 when the developer reaches a position corresponding to the distance x in the axial direction of the screw shaft 51 from the boundary line Lc are θra and θrb, respectively. To do. The arrival angles θra and θrb are as shown in FIG. The relationship shown in the following formula 10 is satisfied for all x in the range shown in the formula 8.

[Equation 10]
θd−θra = (γ−1) × 360 × (x / p) −αa (x) = 0.43 × 360 × (x / 40) −149.86 ≠ 0
And θd−θrb = (γ−1) × 360 × (x / p) −αb (x) = 0.43 × 360 × (x / 40) + 30.14 ≠ 0

  As shown in FIG. 21, the long shaft portion 41a of the rib member 41 reaches a position where the developer corresponds to a distance x in the axial direction of the screw shaft 51 from the boundary line Lc. At this time, the developer splashed by the downstream end portion U of the screw blade 51a is rotated within a range where the straight line indicating the arrival angle θra of one of the long shaft portions 41a of the rib member 41 is within the range shown in the equation (8). Does not intersect the straight line indicating the angle θd.

  Thus, the developer splashed by the downstream end portion U of the screw blade 51a is not caught up by the long shaft portion 41a of the rib member 41 while passing through the region where the long shaft portion 41a of the rib member 41 is present. . As a result, the developer bounced up at the downstream end portion U of the screw blade 51a is not further bounced up by the long shaft portion 41a of the rib member 41. As a result, the developer does not leak from the discharge port 40.

  However, as shown in FIG. 21, the other long shaft portion 41b of the rib member 41 reaches a position corresponding to the axial distance x of the screw shaft 51 from the boundary line Lc. At this time, the developer sprung up by the downstream end portion U of the screw blade 51a rotates within a range where the straight line indicating the arrival angle θrb of the other long shaft portion 41b of the rib member 41 is within the range shown in the equation (8). Intersects with a straight line indicating the angle θd.

  As a result, the developer splashed at the downstream end portion U of the screw blade 51a is caught up by the long shaft portion 41b of the rib member 41 while passing through the region where the long shaft portion 41b of the rib member 41 is present. As a result, the developer bounced up at the downstream end portion U of the screw blade 51a is further bounced up by the long shaft portion 41b of the rib member 41. Thereby, there is a high possibility that the developer overflows out of the discharge port 40.

<Measurement of amount of developer leaking from outlet>
FIG. 22A shows the amount of developer leaking from the discharge port 40 of this embodiment shown in FIG. FIG. 22B shows the amount of developer leaking from the discharge port 40 of the comparative example shown in FIG. The amount of developer leaking from the discharge port 40 can be measured as follows.

  First, with the developing sleeve 28 and the first and second conveying screws 25 and 26 being rotated at a predetermined peripheral speed, the developing container 22 is coated until the developer is uniformly coated on the surface of the developing sleeve 28. Put the developer inside. Next, the developing sleeve 28 and the first and second conveying screws 25 and 26 are rotationally driven at a predetermined peripheral speed until the developer circulation in the developing container 22 reaches a steady state. Usually, it is rotated for about 1 minute to 2 minutes.

  Next, after the developer coating has become uniform on the surface of the developing sleeve 28, the developer is gradually put into the developing container 22 from the replenishing port 30 shown in FIG. The amount of developer discharged per unit time is measured.

  In this embodiment, 10 g of developer is put into the developing container 22 from the replenishing port 30 shown in FIG. 3, and the discharge amount of the developer discharged from the discharge port 40 is measured for 30 seconds. Thereby, the discharge amount per unit time of the developer discharged from the discharge port 40 was measured.

  In the present embodiment shown in FIG. 22A and the comparative example shown in FIG. 22B, the developer discharge amount increases as the developer amount increases. However, in the comparative example shown in FIG. 22B, there is a point e where the developer discharge amount reaches a peak before the developer discharge amount increases in earnest. This is because when the amount of developer is small, the developer is splashed up at the downstream end portion U of the screw blade 51a, and then collides with the rib member 41 and overflows from the discharge port 40. .

  On the other hand, in the case of this embodiment shown in FIG. 22A, the rib member 41 is installed at a phase angle α (x) that escapes the developer splashed by the downstream end U of the screw blade 51a. Yes. Therefore, there is no point e where the developer discharge amount reaches a peak as in the comparative example shown in FIG.

  As a result, in the case of the present embodiment shown in FIG. 22A, only the truly surplus developer is discharged from the discharge port 40. Accordingly, it is possible to stably coat the developer on the surface of the developing sleeve 28 over a long period of time, and to suppress image adverse effects such as image density unevenness.

  In the present embodiment, the screw shaft 51 is provided with a protrusion such as a small diameter screw or a member for exciting the developer. Even in that case, the developer is prevented from jumping up and discharged, and only the developer that is truly surplus is discharged. As a result, the developer is stably coated on the surface of the developing sleeve 28 over a long period of time, and image adverse effects such as image density unevenness are suppressed.

K ... second straight line L1, L2 ... distance Lc in the axial direction of the screw shaft from the boundary line between the upstream end portion and the downstream end portion of the rib member ... boundary line N ... first straight line o ... rotation center p of the screw shaft ... Spiral pitch x of screw blades ... Distance in the axial direction of the screw shaft with reference to the boundary line
40… discharge port
41 ... Rib member (protrusion)
41g ... Conveying surface
41h… Upstream end
41i ... downstream end
51, 52 ... Screw shaft (rotary shaft)
51a, 52a ... Screw blade (blade part)
51b ... Conveying surface
51d ... outer peripheral surface of screw blade

Claims (4)

A developer carrier on which a developer having toner and magnetic particles is carried;
A circulation path through which the developer supplied to the developer carrier circulates while being stirred;
Replenishment means for replenishing at least magnetic particles to the circulation path;
A discharge port provided on the circulation path, through which a part of the circulating developer overflows and is discharged;
A rotation shaft rotatably provided in a circulation path facing the discharge port, a conveyance member including a protrusion and a blade portion formed around the rotation shaft,
Have
The transport member, with respect to the axial direction of the rotating shaft, a first region including at least a portion facing the discharge port, a second region adjacent to the first region,
Have
The protrusion formed in the first region has a smaller outer diameter than the blade portion formed in the second region,
The protrusion formed in the first region is
The distance in the axial direction of the rotating shaft with respect to the end point on the most upstream side of the circulation path of the first region is x,
A distance in the axial direction of the rotating shaft between an end point on the most upstream side of the circulation path in the first region and an upstream end point in the developer circulation direction of the protrusion formed in the first region. To L1,
A distance in the axial direction of the rotating shaft between an end point on the most upstream side of the circulation path in the first region and an end point on the downstream side in the developer circulation direction of the protrusion formed in the first region. To L2,
The moving speed in the rotation direction of the transport member of the developer transported by the transport member at the boundary portion entering the first region from the second region is determined by the rotation direction of the transport member on the outer peripheral surface of the transport member. The value divided by the moving speed of γ,
The helical pitch of the conveying member is p,
When the rotation direction of the transport member is positive, the outer peripheral point of the blade portion in the cross section of the blade portion of the transport member at the boundary portion entering the first region from the second region, and the transport member A first straight line passing through the rotation center of the rotation shaft and a cross section at a distance x in the protrusion formed in the first region at a predetermined height position on the developer conveyance surface of the protrusion. An angle formed by a certain point and the second straight line passing through the rotation center of the rotation axis is α (x),
Then,
In all x of L1 ≦ x ≦ L2,
(Γ−1) × 360 × (x / p) −α (x) ≠ 0
A developing device characterized by satisfying the above.   2. The development according to claim 1, wherein the point at the predetermined height position is a point at a height position of 8/10 of the highest point on the basis of the outer peripheral surface of the rotation shaft of the protrusion. apparatus.   The average angle formed between the developer conveyance surface of the protrusion formed in the first region and the rotation axis is the developer conveyance surface of the blade portion formed in the second region and the rotation. The developing device according to claim 1, wherein the developing device is set to be smaller than an average angle formed by the shaft. The developing device according to any one of claims 1 to 3,
An image carrier for carrying an electrostatic latent image;
Have
An image forming apparatus comprising: supplying a developer to an electrostatic latent image carried on the image carrier by the developing device to form an image.

Images